Codes transcriptionnels et expression du gène du récepteur de la GnRH au cours du développement et chez l'adulte

Le récepteur hypophysaire de la GnRH (RGnRH) joue un rôle crucial dans le contrôle de la fonctionde reproduction. Dans le promoteur distal du Rgnrh, j ai caractérisé un élément de réponsebifonctionnel répondant aux protéines LIM à homéodomaine ISL1/LHX3 et à GATA2. D autre part,deux motifs TAAT situés dans la région plus proximale confèrent à ce gène la capacité de répondreaux facteurs Paired-like PROP1 et OTX2. Tous ces facteurs, exprimés précocement au cours del ontogenèse hypophysaire, pourraient participer à l émergence de l expression du Rgnrh. Hors del hypophyse, j ai découvert que le Rgnrh est exprimé au cours du développement postnatal dansl hippocampe de rat, où il module la plasticité synaptique. Par ailleurs, j ai identifié deux nouveauxsites d expression, la rétine et la glande pinéale. Ces résultats mettent en lumière l importancefonctionnelle de ce récepteur et de son ligand et les rôles multiples qu il ont acquis au cours del évolution des Vertébrés.In the pituitary, the GnRH receptor (GnRHR) plays a crucial role in the neuroendocrine control ofreproductive function. Within the distal region of the Gnrhr promoter, I have characterized abifunctional response element modulated by the LIM homeodomain proteins ISL1/LHX3 and byGATA2. Besides, in the proximal region of the promoter, two TAAT motifs conferred response toPaired-like factors PROP1 and OTX2. All these factors are expressed during pituitary ontogenesis andcould participate in the onset and regulation of Gnrhr expression. Outside of the pituitary, I havediscovered that the Gnrhr was expressed during postnatal development in the rat hippocampus, whereit modulated synaptic plasticity. Furthermore, I have identified two novel sites of Gnrhr expression, theretina and the pineal gland. Altogether, these data highlight the functional importance of this receptorand its ligand as well as the multiple roles they have acquired during vertebrate evolution.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Preferential role of calcium in the regulation of prolactin gene transcription by thyrotropin-releasing hormone in GH3 pituitary cells

TRH induces two separate events in pituitary PRL cells. It increases the release of stored PRL and enhances the rate of PRL gene transcription, which results in an increased steady state concentration of PRL messenger RNA (mRNA) and a concomitant augmentation of PRL production. The mechanisms underlying the release process involve the activation of phosphatidylinositol turnover which generates inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. In order to determine whether these intracellular messengers also mediate the stimulation of PRL gene expression by TRH, we have correlated the level of receptor occupancy with the rate of gene transcription and investigated the action of drugs which increase cytosolic calcium or activate protein kinase C. We have determined that sustained stimulation of transcription requires the persistent occupancy of a limited number of TRH receptor sites and that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), calcium ionophores (A23187, ionomycin), and the calcium channel agonist BAY K 8644 enhance PRL gene transcription. However, TPA is less potent and ionomycin requires a low concentration of TPA to fully mimic TRH action, whereas BAY K 8644 alone displays the same potency as TRH. The effects of BAY K 8644 and TRH are not additive and thus suggest that the influx of calcium plays a predominant role in the regulation of PRL gene transcription by TRH

Differential implication of deoxyribonucleic acid methylation in rat prolactin and rat growth hormone gene expressions: a comparison between rat pituitary cell strains

In order to assess the potential role of DNA methylation in the expression of rat PRL (rPRL) as compared to rat GH (rGH) gene, the cleavage patterns generated by the isoschizomeric restriction enzymes HpaII and MspI were examined in DNA isolated from rat pituitary cell lines producing either high levels of rPRL (GH3B6) or of rGH (GC) and in a stable variant cell strain which produces minute amounts of both hormones (GH3CDL cells). The rPRL and the rGH genes were found hypomethylated in GH3B6 and GC cells, respectively, whereas in GH3CDL cells both genes were methylated, indicating a correlation between the extent of gene methylation and the level of expression. However the use of 5-azacytidine (5-azaC), which decreases DNA methylation, suggested a variable importance of gene methylation in the control of rPRL and rGH gene expression. 5-AzaC was unable to increase rPRL production to a detectable level in GC cells, whereas the cytidine analog markedly increased rPRL production and rGH production in GH3CDL cells. Further analysis using GH3CDL cells showed that the extent of the 5-azaC-induced rPRL and rGH gene demethylation was consistent with the 5-azaC-induced increase of gene expressions. However, in these cells, the stimulation of rPRL and rGH production unexpectedly increased as a function of time elapsed after drug withdrawal. The maximal stimulation, 30-fold and 7-fold, respectively, was observed 3 weeks after a 60-h exposure to 5-azaC. This pattern suggests that other events are required for the full expression of rPRL and rGH genes in addition to their own demethylation

Tertiary lymphoid structures in epithelioid malignant peritoneal mesothelioma are associated with neoadjuvant chemotherapy, but not with prognosis

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